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2010, Vol. 19, No. 4　Online: 2010-07-30

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Low-temperature CO oxidation over CuO-CeO2/SiO2 catalysts: Effect of CeO2 content and carrier porosity Jingjie Luo;Wei Chu*;Huiyuan Xu;Chengfa Jiang*;Tao Zhang 2010, 19(4): 355-361.  DOI: 摘要 ( 8526 )   PDF   The effects of CeO2 contents and silica carrier porosity with their pore diameters ranging from 5.2 nm to 12.5 nm of CuO-CeO2/SiO2 catalysts in CO oxidation were investigated. The catalysts were characterized by N2 adsorption/desorption at low temperature, X-ray diffraction (XRD), temperature-programmed reduction by H2 (H2-TPR), oxygen temperature programmed desorption (O2-TPD) and X-ray photoelectron spectroscopy (XPS). The results suggested that, the ceria content and the porosity of SiO2 carrier possessed great impacts on the structures and catalytic performances of CuO-CeO2/SiO2 catalysts. When appropriate content of CeO2 (Ce content \leqslant 8 wt%) was added, the catalytic activity was greatly enhanced. In the catalyst supported on silica carrier with larger pore diameter, higher dispersion of CuO was observed, better agglomeration-resistant capacity was displayed and more lattice oxygen could be found, thus the CuO-CeO2 supported on Si-1 showed higher catalytic activity for low-temperature CO oxidation.

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Kinetics of the water-gas shift reaction in Fischer-Tropsch synthesis over a nano-structured iron catalyst Ali Nakhaei Pour;*;Mohammad Reza Housaindokht;Sayyed Faramarz Tayyari;Jamshid Zarkesh 2010, 19(4): 362-368.  DOI: 摘要 ( 9332 )   PDF   Based on formate and direct oxidation mechanisms, three Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic models of the water-gas-shift (WGS) reaction over a nano-structured iron catalyst under Fischer-Tropsch synthesis (FTS) reaction conditions were derived and compared with those over the conventional catalyst. The conventional and nanostructured Fe/Cu/La/Si catalysts were prepared by co-precipitation of Fe and Cu nitrates in aqueous media and water-oil micro-emulsion, respectively. The WGS kinetic data were measured by experiments over a wide range of reaction conditions and comparisons were also made for various rate equations. WGS rate expressions based on the formate mechanism with the assumption that the formation of formate is rate determining step were found to be the best.

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Effect of O2 and H2O on the tri-reforming of the simulated biogas to syngas over Ni-based SBA-15 catalysts Daoan Sun;Xiujin Li;Shengfu Ji*;Lingyan Cao 2010, 19(4): 369-374.  DOI: 摘要 ( 10439 )   PDF   A series of Ni/SBA-15 catalysts with Ni contents from 7.5 wt% to 15 wt% were prepared by impregnation method. The effect of O2 and H2O on the combined reforming of the simulated biogas to syngas was investigated in a continuous flow fixed-bed micro-reactor. The stability of the catalyst was tested at 800 ℃. The results indicated that 10 wt%Ni/SBA-15 catalyst exhibited the highest catalytic activities for the combined reforming of the simulated biogas to syngas. Under the reaction conditions of the feed gas molar ratios CH4/CO2/O2/H2O = 2/1/0.6/0.6, GHSV = 24000 ml•g{cat}-1\cdoth-1 and the reaction temperatureT = 800 ℃, the conversions of CH4 and CO2 were 92.8% and 76.3%, respectively, and the yields of CO and H2 were 99.0% and 82.0%, respectively. The catalytic activities of the catalyst did not decrease obviously after 100 h reaction time on stream.

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Conversion of natural gas to C2 hydrocarbons via cold plasma technology Jing Lv;Zhenhua Li 2010, 19(4): 375-379.  DOI: 摘要 ( 9854 )   PDF   The plasma technology served as a tool in unconventional catalysis has been used in natural gas conversion, because the traditional catalytic methane oxidative coupling reaction must be performed at high temperature on account of the stability of methane molecule. The focus of this research is to develop a process of converting methane to C2 hydrocarbons with non-equilibrium plasma technology at room temperature and atmospheric pressure. It was found that methane conversion increased and the selectivity of C2 hydrocarbons decreased with the voltage. The optimum input voltage range was 40--80 V corresponding to high yield of C2 hydrocarbons. Methane conversion decreased and the selectivity of C2 hydrocarbons increased with the inlet flow rate of methane. The proper methane flow rate was 20--40 ml/min (corresponding residence time 10--20 s). The experimental results show that methane conversion was 47% and the selectivity of C2 hydrocarbons was 40% under the proper condition using atmospheric DBD cold plasma technology. It was found that the breakdown voltage of methaneV\rmB was determined by the type of electrode and the discharge gap width in this glow discharge reactor. The breakdown voltage of methaneV{B, {min}} derived from the Paschen law equation was established.

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A model for estimating flow assurance of hydrate slurry in pipelines Wuchang Wang*;Shuanshi Fan;Deqing Liang;Yuxing Li 2010, 19(4): 380-384.  DOI: 摘要 ( 8940 )   PDF   The problem of hydrate blockage of pipelines in offshore production is becoming ever-increasing severe because oil fields in ever-increasing unusual environments have been brought in production. HCFC-141b and THF were selected as the substitutes to study the flow assurance of the hydrates in pipelines. There are critical hydrate volume concentrations for these two slurries. Hydrate slurries behave like Bingham fluids and have high agglomerating tendency when the hydrate volume concentrations are larger than the critical ones. Based on rheological behaviors of these two hydrates, a non-dimensional parameter is proposed through studying the driving forces of agglomeration among hydrate particles, which shows the agglomerating probability of hydrate particles in pipeline and can be used to judge the safety of the pipeline. Moreover, a safe model to judge the safely flow hydrate slurries was presented and verified with the experimental data, which demonstrates that the model is effective to judge whether the pipeline can be run safely or not.

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Kinetic simulation of oxidative coupling of methane over perovskite catalyst by genetic algorithm: Mechanistic aspects Nastaran Razmi Farooji*;Ali Vatani;Shahrnaz Mokhtari 2010, 19(4): 385-392.  DOI: 摘要 ( 9687 )   PDF   The reaction kinetics of oxidative coupling of methane catalyzed by perovskite was studied in a fixed bed flow reactor. At atmospheric pressure, the reactions were carried out at 725, 750 and 775 ℃, inlet methane to oxygen ratios of 2 to 4.5 and gas hourly space velocity (GHSV) of 100 min-1. Correlation of the kinetic data has been performed with the proposed mechanisms. The selected equations have been regressed with experimental data accompanied by genetic algorithm (GA) in order to obtain optimized parameters. After investigation the Langmuir-Hinshelwood mechanism was selected as the best mechanism, and Arrhenius and adsorption parameters of this model were obtained by linear regression. In this research the Marquardt algorithm was also used and its results were compared with those of genetic algorithm. It should be noted that the Marquardt algorithm is sensitive to the selection of initial values and there is possibility to trap in a local minimum.

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Low temperature H2S sensor based on copper oxide/tin dioxide thick film Hongbing Wei;Hongwen Sun;Sumei Wang;Guangzhi Chen;Yingtao Hou;Hongwen Guo;Xiaodong Ma* 2010, 19(4): 393-396.  DOI: 摘要 ( 10379 )   PDF   Nanostructured tin dioxide (SnO2) powders were prepared by a sol-gel dialytic process and and the doping of CuO on it was completed by a deposition-precipitation method. The thick film sensors were fabricated from the CuO/SnO2 polycrystalline powders. Sensing behavior of the sensor was investigated with various gases including CO, H2, NH3, hexane, acetone, ethanol, methanol and H2S in air. The as-synthesized gas sensor had much better response to H2S than to other gases. At the same time, the CuO/SnO2 sensor had enough sensitivity, together with fast response and recovery, to distinguish H2S from those gases at 160 and 210 ℃. Therefore, it might have promising applications in the future.

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Composite surfactants aided solvothermal synthesis and catalytic hydrogenation property of oil soluble bimetallic CoMoS nanoparticles Shutao Wang;Changhua An*;Jie He;Zongxian Wang;Jikang Yuan; 2010, 19(4): 397-402.  DOI: 摘要 ( 11929 )   PDF   Oil-soluble bimetallic CoMoS nanoparticles were successfully synthesized by a composite-surfactants-aided-solvothermal process. The surface hydrophilicity and functionality of the products were investigated through transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectra, and Ultraviolet (UV) spectra analysis. The catalytic performance of hydrogenation on the CoMoS nanoparticles was studied with naphthalene as a model compound. It was found that CoMoS catalysts supported on active carbon (AC) was more active than conventional MoS2/γ-Al2O3. The activity of CoMoS/AC can be tailored through the change of the Co/(Co+Mo) atomic ratio.

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Characteristics of gaseous product from municipal solid waste gasification with hot blast furnace slag Lumei Zhao;Hua Wang*;Shan Qing;Huili Liu 2010, 19(4): 403-408.  DOI: 摘要 ( 8815 )   PDF   Possibility of combustible gas production from municipal solid waste (MSW) using hot blast furnace (BF) slag has been studied. The objective of this work is to generate combustible gas from MSW using heated BF slag. In this experiment, the thermal stability of the MSW was analyzed by thermogravimetric analysis, and effects of temperature, gasifying agent (air, N2, steam) and BF slag on the gas products were investigated at 600-900 ℃. The thermogravimetric analysis indicates that the weight loss of MSW includes four stages: evaporation of the moisture, combustion of volatile materials, burning of carbon residue and burnout of ash. The contents of the combustible gas increase with increasing temperature, and the lower calorific value (LCV) increases rapidly at 600-900 ℃. It is found that volume fraction of CO, H2 and CH4 at different atmospheres increases in the order N2

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Reaction and deactivation kinetics of methanol-to-olefins process based on a special TGA reactor Hao Hu;Weiyong Ying;Dingye Fang;* 2010, 19(4): 409-416.  DOI: 摘要 ( 10217 )   PDF   Thermax 700 thermo gravimetric analysis (TGA) instrument is introduced for the investigation of the reaction and deactivation kinetics of Methanol-to-Olefins (MTO) process with SAPO-34 catalyst. By the use of a special sample basket, the TGA instrument can be viewed as a plug flow fixed-bed reactor, while the weight change of SAPO-34 during reaction can be recorded online. Kinetic data are acquired in the temperature range of 648.2-748.2 K and space velocities of 7.08-35.91 h-1 (WHSV). Catalyst activity is expressed with average coke content, and selectivity for different products is related as a function of coke content and temperature. Methane is also introduced into the lumping kinetic model, and power exponent function with first-order reaction is adopted for model deduction. Exponential function is tested to give the best fit for catalyst activity and product selectivity with the highest correlation coefficient. The nicely agreed results between experimental and calculated data suggest that the overall kinetic model would be meaningful in both product distribution prediction and reactor simulation.

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Pd/Hβ-zeolite catalysts for catalytic combustion of toluene: Effect of SiO2/Al2O3 ratio Zekai Zhang;Longya Xu;Zhanlong Wang;Yujuan Xu;Yinfei Chen* 2010, 19(4): 417-421.  DOI: 摘要 ( 9500 )   PDF   The effect of pure and high silica Hβ zeolites on the catalytic performance of toluene combustion over Pd/Hβ catalyst was evaluated. Pure and high silica β zeolites were prepared by direct synthesis procedures, then 0.1 wt% of palladium was impregnated on different Hβ zeolites via incipient wetness technique using palladium nitrate as the Pd source. The Pd/Hβ catalysts were characterized by XRD, N2 adsorption/desorption, H2O adsorption, NH3-TPD, H2-TPR and XPS techniques. With increasing the SiO2/Al2O3 ratio of β zeolite, the activity of the Pd/Hβ catalysts for toluene combustion increased clearly and the pure silica β zeolite supported Pd catalyst showed the best catalytic activity. The superior catalytic performance of Pd/β catalyst prepared from pure silica β zeolite was attributed to its high hydrophobicity and the preserving ability for PdO active species.

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Performance and characterization of iron-nickel catalysts for light olefin production Mostafa Feyzi;Ali Akbar Mirzaei* 2010, 19(4): 422-430.  DOI: 摘要 ( 9233 )   PDF   A series of x (Fe, Ni)/Al2O3 catalysts (x = 2--12 wt%) were prepared using incipient wetness method and studied for the conversion of synthesis gas to light olefins. 6 wt%(Fe, Ni)/Al2O3 catalyst was found to be the optimal catalyst for the production of C2--C4 olefins. The effects of calcination behaviors and operational conditions on the catalytic performance of the optimal catalyst were investigated. The best operational conditions were molar feed ratio H2/CO = 2/1, T = 260 ℃, gas hourly space velocity (GHSV) = 2600 h-1 and the pressure of 3 bar. Characterizations of both precursors and catalysts were carried out using X-ray diffraction (XRD), temperature-programmed reduction (TPR), scanning electron microscopy (SEM), N2-adsorption-desorption measurement, thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC).

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Chitosan as green kinetic inhibitors for gas hydrate formation Yongjun Xu*;MinlinYang;Xiaoxi Yang 2010, 19(4): 431-435.  DOI: 摘要 ( 9502 )   PDF   The kinetic inhibiting effect of a number of chitosans on hydrate formation was investigated using methane and methane/ethane gas mixtures. The results indicated that chitosan was a good kinetic inhibitor. The induction time of gas hydrate formation evidently increased with the degree of deacetylation (DD), however, when DD washigher than 80%, the effect of DD on the induction time was negligible. Moreover, it was found that the molecular weight (MW) of chitosan and the addition of polyethylene oxide (PEO) had little effect on the induction time. The optimal concentration of chitosan was found to be 0.6 wt%. Finally, the mechanisms of the kinetic inhibitor on the hydrate formation were discussed.

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Kinetic model of transesterification of diphenyl carbonate and 1, 4-butyldiol Liping Wang;;Bin Xiao;;Gongying Wang 2010, 19(4): 436-440.  DOI: 摘要 ( 11034 )   PDF   The transesterification of diphenyl carbonate (DPC) with 1, 4-butyldiol (BD) was kinetically investigated in the presence of lithium acetate catalyst at 465 K. The reaction was followed by the measurement of the quantity of phenol which was distilled from the reactor. The experiments supported the assumption that the phenyl ester groups in DPC and phenyl hdroxybutyl carbonate (PHBH) had the same reactivity, and the transesterification obeyed first-order kinetics with respect to DPC and BD, and a rate equation was derived. The reaction rate was found to be first order with respect to the catalyst concentration as well. When those data were incorporated in the rate equation, excellent agreement between calculated values and the observed ones was recognized over a wide range.

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Kinetics studies of nano-structured iron catalyst in Fischer-Tropsch synthesis Ali Nakhaei Pour;*;Mohammad Reza Housaindokht;Sayyed Faramarz Tayyari;Jamshid Zarkesh 2010, 19(4): 441-445.  DOI: 摘要 ( 9871 )   PDF   Kinetic parameters of nano-structured iron catalyst in Fischer-Tropsch synthesis (FTS) were studied in a wide range of synthesis gas conversions and compared with conventional catalyst. The conventional Fe/Cu/La catalyst was prepared by co-precipitation of Fe and Cu nitrates in aqueous media and Fe/Cu/La nanostructure catalyst was prepared by co-precipitation in a water-in-oil micro-emulsion. Nano-structured iron catalyst shows higher FTS activity. Kinetic results indicated that in FTS rate expression, the rate constant (k) increased and adsorption parameter (b) decreased by decreasing the catalyst particle size from conventional to nano-structured. Since increasing in the rate constant and decreasing in the adsorption parameter affected the FTS rate in parallel direction, the particle size of catalyst showed complicated effects on kinetic parameters of FTS reaction.

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Memory effect on the pressure-temperature condition and induction time of gas hydrate nucleation Qiang Wu;Baoyong Zhang* 2010, 19(4): 446-451.  DOI: 摘要 ( 11516 )   PDF   The focus of this study is to investigate the influence of memory effect and the relation of its existence with the dissociation temperature, using gas hydrate formation and dissociation experiments. This is beneficial because memory effect is considered as an effective approach to promote the thermodynamic and dynamic conditions of gas hydrate nucleation. Seven experimental systems (twenty tests in total) were performed in a 1 L pressure cell. Three types of hydrate morphology, namely massive, whiskery and jelly crystals were present in the experiments. The pressures and temperatures at the time when visual hydrate crystals appeared were measured. Furthermore, the influence of memory effect was quantified in terms of pressure-temperature-time (p-T-t) relations. The results revealed that memory effect could promote the thermodynamic conditions and shorten the induction time when the dissociation temperature was not higher than 25 ℃. In this study, the nucleation superpressure and induction time decrease gradually with time of tests, when the earlier and the later tests are compared. It is assumed that the residual structure of hydrate dissociation, as the source of the memory effect, provides a site for mass transfer between host and guest molecules. Therefore, a driving force is created between the residual structures and its surrounding bulk phase to promote the hydrate nucleation. However, when the dissociation temperature was higher than 25 ℃, the memory effect vanished. These findings provide references for the application of memory effect in hydrate-based technology.